Certain integrated circuits (ICs), such those produced to perform radio frequency (RF) and mixed signal (MS) functions, utilize passive components such as diodes, inductors, and capacitors to generate or modify the necessary high frequency signals. These passive components require a high quality factor, but their quality factor is often reduced by capacitive coupling to a resistive substrate. For example, the capacitive and inductive coupling of an inductor to the resistive substrate will reduce the quality factor of an inductor. Also, the substrate may contain noisy currents generated by digital circuits. Via the coupling to the substrate this noise may be injected to the RF or analog circuit through the passive component, thus degrading the circuits performance.
Schottky diodes are utilized in RF and MS ICs, for example, to produce voltage multipliers and RF mixers. However, the operation of Schottky diodes that are made using conventional methods suffers from parasitic capacitance and leakage to the underlying substrate. Such a leakage path can bypass the diode, degrading the diode's rectifying or nonlinear behavior.
What is needed is a method for fabricating Schottky diodes for RF and MS circuits whereby the parasitic capacitance and leakage to the underlying substrate is substantially reduced. What is also needed is a method for producing such Schottky diodes in a standard CMOS processing flow and in a manner that reduces the number of additional processing steps, thus maintaining the lowest production cost possible for such a diode and the circuits incorporating the diode.